In the formation of metal parts, one very common forming technique is a stamping operation utilizing die and tool sets. Frequently, the forming operation includes a series of dies or tools through which the part passes successively to move from a blank form to a final form, with each stamping operation excessively deforming or performing some other operation on the blank part until it reaches its final desired configuration.
During stamping operations, in many cases it is desirable to measure the load being applied to the tool of the die set during certain stamping operation. The load is monitored on various forms of monitoring equipment, such as oscillographs or recorders, or analyzed using various electronic systems to determine whether the process is being carried out within pre-selected limits or parameters and give an indication of any problems which are developing or have developed.
One common technique for measuring the force during stamping operations or blanking operations is by the use of various types of load cells. These load cells can take several different forms. One form utilizes piezo electric crystals which often are embedded in the tooling and are monitored to give an indication of the force by measuring electrical output as a function of the compression of the crystals.
This is a relatively inefficient technique and does not give high precision required for many operations.
Another technique which is utilized during blanking or forming operations, especially of can lids, is by the use of strain gauge load cells. In one particular prior art application, the load cell utilizes a spool member having strain gauges arranged around the periphery of this spool between the flanges at the opposite ends of the spool. The strain gauges are then potted with epoxy potting material. Wiring extends from the strain gauges to sense the movement or compression of the spool during forming operations. The load cell, is in turn connected between a tool and a tooling base.
The various prior art systems of interfacing the load cell to the tooling have drawbacks. In many, the wiring from the sensor is exposed. This exposure often results in premature failure of the sensor due to mishandling or rough treatment of the product during the course of normal maintenance. For example, die stations tend to accumulate metal fragments and other debris, which must be cleaned periodically. It is not uncommon for a screwdriver or putty knife to be hastily scraped between tooling to remove such debris, which scraping can sever wiring or cut into wiring insulation.
In other prior art systems, a specialized mounting piece is used, which requires a differently configured mounting piece for each tool. This adds cost to a system. In still other prior art systems, the tool itself contains the strain gauges and thus becomes the load cell; this adds cost, since the entire unit might need to be scrapped if either the tool or the sensor fails. Thus, there is a need for an improved system of interfacing load cells to tooling.